节点文献
微波—热泵联合干燥硫酸铵特性及新工艺研究
【作者】 李长龙；
【导师】 彭金辉；
【作者基本信息】 昆明理工大学 ， 有色金属冶金， 2010， 硕士
【摘要】 目前,为了有效解决火电、冶金等行业排放的大量低浓度SO2,大多数企业采用氨法脱硫工艺实现SO2的回收利用。氨法脱硫工艺中经离心脱水后的硫酸铵一般含水率较高,而国标(GB535-1995)中对硫酸铵的含水率具有严格要求,其中优等品的含水率≤0.2%,所以其后续的干燥工艺就很重要。由于现有硫酸铵干燥方式的能耗较高,本研究将微波和热泵技术应用于硫酸铵的干燥,深入研究硫酸铵的微波干燥特性,建立硫酸铵微波干燥的动力学模型,并研究不同干燥工艺能效比的变化规律,通过系统实验确定硫酸铵热泵-微波联合干燥的优化工艺条件,为实现硫酸铵微波干燥的产业化应用提供了理论依据。具体工作如下：首先,开展了微波干燥硫酸铵的研究。通过系统实验分析了硫酸铵微波干燥特性,并采用薄层干燥模型进行数值分析。结果表明,修正page模型(Ⅱ)较之其他模型更适于薄层硫酸铵微波干燥的模拟。应用Fick第二定律得到微波功率230-700W,物料质量150-300g条件下薄层硫酸铵微波干燥的有效扩散系数的变化范围分别为：1.48×10-7～4.33×10-7m2/s,3.61×10-7-6.59×10-7m2/s。其次,为实现微波基础条件下的节能降耗,探索微波控温干燥硫酸铵的工艺。探讨了干燥温度、微波干燥时间、物料质量、物料厚度等因素对硫酸铵相对脱水率的影响；以硫酸铵的相对脱水率为响应值采用响应曲面中心组合设计,对硫酸铵的微波干燥工艺参数进行了优化。所获得的优化实验条件为：干燥温度86.05℃,微波干燥时间190.50s,物料质量102.59g,物料厚度20.55mm,此时物料的相对脱水率为99.29%,验证实验的实验值与预测值的偏差仅为-0.43%,可靠性高。与常规干燥的对比研究表明,在相同条件下(相同物料质量、干燥温度以及物料厚度,达到相同相对脱水率)微波控温干燥较之常规干燥节时77.14%。另外,为进一步降低硫酸铵的干燥能耗,开展热泵干燥硫酸铵的工艺研究。探讨了物料质量、干燥时间、物料厚度对相对脱水率和能效比的影响；并以硫酸铵的相对脱水率和能效比为响应值采用响应曲面中心组合设计,对硫酸铵的热泵干燥工艺参数进行了优化。所获得的优化实验条件为：物料质量598.9g,热泵干燥时间56.75min,物料厚度15mm,此时物料的相对脱水率为91.79%,能效比为0.304kg/kwh。回归分析和验证试验表明了该响应面法的合理性与可行性。与常规干燥的对比研究表明,在相同条件下热泵干燥不仅具有明显的节能优势还具有一定的节时优势(24.33%)。在以上系统实验的基础上,通过对微波、热泵干燥条件下相对脱水率与能效比的对比分析,确定了可行的热泵-微波联合干燥工艺的水平范围；并以硫酸铵的相对脱水率和能效比为响应值采用响应曲面中心组合设计,对硫酸铵的联合干燥工艺参数进行了优化。所获得的优化实验条件为：物料质量600g,热泵干燥时间37.26min,微波干燥时间1min,此时物料的相对脱水率为91.7%,能效比为0.316kg/kwh。与单独热泵、微波干燥实验的比较分析表明：联合干燥较之热泵干燥在能效比方面提高9.93%,节时32.58%；较之微波干燥能效比提高45.91%。
【Abstract】 At present, in order to deal with massive low concentration SO2 exhausted by thermal power and metallurgy industry, majority enterprises adopt the ammonia desulphurization technology to realize the recycle of SO2. In the ammonia desulphurization technology, centrifugal dewatered ammonium sulfate usually contains high water ratio. However, in national standard (GB535-1995), there is a strict provision of the ammonium sulfate’s moisture content, in which the moisture content of premium grades is less than 0.2%. For the reasons above, the following drying process is significant and necessary. Because of the high energy consumption in current ammonium sulfate drying process, the microwave and heat-pump drying technology is applied to ammonium sulfate drying in this research. In this article, ammonium sulfate’s microwave drying characteristic was in-depth studied, and the drying dynamics model was established. Meanwhile under the study of the energy efficiency compared to different drying process, the heat pump-microwave combined drying craft of ammonium sulfate and the best technological conditions were determined, providing the important theory basis to realize the industrial production application of ammonium sulfate’s microwave drying.Firstly, the research on microwave drying of ammonium sulfate technique was initiated.The drying behavior of ammonium sulfate was investigated and the thin-layer drying models are used for data processing. The results show that the modified page model (II) is more suitable than other models for simulation of microwave drying of ammonium sulfate. Under the condition of microwave power of 230-700W or material mass being 150-300g, application of Fick’s second law results in an effective diffusion coefficient of thin-layer sludge subjected to microwave drying ranging from 1.48×10-7 to 4.33×10-7m2/s or from 3.61×10-7 to 6.59×10-7m2/s, respectively.Secondly, for realizing the low energy consumes under the basic conditions of microwave drying, ammonium sulfate technique is investigated, using the temperature-controlled microwave technology. It is indicate that the key factors, like drying temperature, microwave drying time, material weight and thickness, have an affect on the relative dehydration rate of ammonium sulfate. On the basis of single-factor experiment, the response surface central composite design was adopted to optimize microwave drying parameters of ammonium sulfate, by taking the relative dehydration rate of ammonium sulfate as response value. The obtained optimized technology parameters were:temperature of 86.05℃, the radiation time of 190.50s, material weight of 102.59g, thickness of 20.55mm. The corresponding relative dehydration rate of material is 99.29%. The deviation of experimental values and predicted values is only-0.43%, showing high reliability. The results show that the response surface central composite design plays good optimization and prediction roles. The technology of microwave drying of ammonium sulfate used is reasonable and feasible, which can provide reference and guide for future research. The contrast research with the conventional drying indicated that under the condition of the same temperature, material weight, thickness and achieves the same relative dehydration rate, The temperature-controlled microwave drying compared with the conventional drying save the time of 77.14%, and can obvious guarantee the quality of the product at the same time.Besides, the heat-pump drying experiment of ammonium sulfate was carried out to further reduce the energy consumption. The effects of material quality, drying time, material thickness on the relative dehydration rate and the energy efficiency ratio of ammonium sulfate were investigated. On the basis of single-factor experiment, the response surface central composite design was adopted to optimize heat-pump drying parameters of ammonium sulfate, by taking the relative dehydration rate and the energy efficiency of ammonium sulfate as response value. The obtained optimized technology parameters were: material quality 598.9g, heat pump drying time 56.75min, material thickness 15mm. The corresponding relative dehydration rate of material is 92.1%, the energy efficiency ratio is 0.292kg/kw·h. The regression analysis and the verification test have indicated the rationality and the feasibility of the response surface method. The contrast research with the conventional drying shows that under the condition of the same temperature, material weight, thickness and achieves the same relative dehydration rate, the heat pump drying not only has the obvious energy conservation superiority and also has certain timing superiority.On the basis of experiments above, the feasible horizontal extent of heat pump microwave combined drying craft was determined through the contrastive analysis of relative dehydration rate and energy efficiency ratio. And the response surface central composite design was adopted to optimize heat pump-microwave combined drying parameters of ammonium sulfate, by taking the relative dehydration rate and the energy efficiency of ammonium sulfate as response value. The obtained optimized technology parameters were:Material quality of 600g, heat pump time of 37.26min, microwave time of lmin. The corresponding relative dehydration rate of material is 91.7%, the energy efficiency ratio is 0.316kg/kw-h. The contrast research with The separate experiments of heat-pump and microwave drying shows that compared with the heat-pump drying, compared drying can enhances by 12.9% in the energy efficiency ratio, saving the time by 36.2%; Compared to microwave drying, can enhances 43.6% in energy efficiency ratio, simultaneously can guarantee the quality of the product.